DeForest Crosley Model 870 (Rogers Chassis 8M-721)

[Gerry O’Hara]

Just finished restoring a DeForest Crosley Model 870 (‘Greig’). This model has a Rogers Chassis Type 8M-721 fitted – a 7 tube superhet dating from the 1938-39 model year. I ‘found’ this set in three pieces: the chassis (rough and minus some tubes), the cabinet (rather rougher, but miraculously containing a plastic bag with the knobs and other hardware in it) and the dial glass (pristine), under a plastic canopy and lean-to shed ‘somewhere in Agassiz’, BC, back in 2007. I think it set me back $30 – maybe a little high for a ‘scrapper’, but I thought it had potential and I really liked the dial glass markings and shape. The set resided in my garage for over a year before it came to the top of the restoration pile in the VE7GUH shack.

The cabinet was taken to the SPARC museum in Coquitlam, BC, where I proceeded to strip it down (by dry scraping), replace several areas of the veneer (where missing/damaged) and re-glued the frame and some sections of the veneer that had parted from the top of the set. The cabinet was then sanded with 600 grade ‘wet n dry’ lubricated with lemon oil, and then given several coats of shellac, each being rubbed down with super-fine steel wool. Once the grain was filled with the shellac, three coats of clear lacquer were applied all-over the cabinet. The main body of the cabinet was then masked-off, and the sides, dial cut-out and edges of the speaker fretwork given given several coats of dark brown-tinted semi-gloss lacquer. The remainder of the cabinet was then given three coats of brown-tinted lacquer, followed by several coast of clear semi-gloss lacquer over the entire cabinet. This seems like a lot of work, but was necessary to replicate the tones and lustre of the original finish. The wooden knobs were stripped of their old finish and also given several coats of dark brown-tinted lacquer. This process took several weeks, working on Sunday afternoons and occasional Thursday evenings (thanks for all the advice Pat!).

Meanwhile I worked on the chassis at home. This is an interesting one, sporting a Rogers tube set, including two half wave rectifier tubes (2X3s) in place of the more standard ful wave rectifier (eg. 5Y3). The rest of the tube line-up is a 6K7M (RF amp), 6J8M (mixer/oscillator), 6K7M (IF amp), 75M (detector/AGC/1st AF) and 41M (output). The chassis was given a good cleaning – it was painted black at the factory so there was no rust present – and the tuning mechanism – a friction clutch – cleaned of old grease and decades accumulation of filth. The bearings were re-lubed with a little machine oil. The circuit includes two bias cells (see my post on these gadgets elsewhere on this forum) providing delayed AGC and bias for the first AF amp. The bias cell holders had already been modified to take standard modern button cells, so I popped a couple of new cells in as the ones fitted measured only a fraction of a volt. Someone had already had a go at recapping the chassis – by the looks of the replacements this had been done within the last 15 years or so – all polycarb or mylars, but strangely the electrolytics had not been replaced – these were very leaky and well out of tolerance, so I replaced them, leaving the old electrolytic can and cardboard casing above the chassis for cosmetics. Several resistors were tested and these were found to be within tolerance so all were left as found. The transformer tested ok as did the loudspeaker field coil (phew!), though the speaker wiring had to be replaced (I have a supply of cloth-covered wire purchased from Radio Daze that made a good job of this). The missing Rogers tubes were sourced from Phil at the CVRS (thanks Phil! – oh, and I still owe him for them…), except the 2X3’s and the 75M. The set had a single 2X3 fitted on arrival, but try as I did, locating a second proved elusive. Becoming impatient after a week or so of completing other repairs on the chassis and having the cabinet ready, I considered fitting a couple of silicon diodes/current limiting resistors (1N4007/150ohm) as a temporary ‘fix’. After some thought, I re-wired the 2X3 rectifier sockets slightly and fitted a 5Y3 in one of the sockets instead. ‘Abbotsfordgerry’ (Gerry) provided some 6Q7’s to try in place of the 75M duo-diode-triode and hey presto! – the set powered-on ok when brought up slowly on my variac. But at first only the output stage seemed to be working. I checked voltages throughout the set and all seemed ok. A little signal-tracing soon found the problem: the previous restoration efforts by ‘anon’ had connected the (replacement) coupling capacitor from the grid of the output stage to ground instead of to the anode of the first AF stage! Once corrected, stations came rolling in on both the Broadcast Band and Shortwaves. A slight, but annoying hum was present when the speaker was mounted in the cabinet (inaudible when on the bench) – later traced to the glass-bodied 6Q7 I had fitted – when I tried a metal-bodied 6Q7 the hum went away (figures, as the original 75M would have had a metallized envelope). While the chassis was out of the cabinet again while troubleshooting the hum I installed an in-line fuseholder (with a 1.5Amp fuse fitted) in the power transformer primary, replaced the rubber mounts on the tuning gang support bracket (I used rubber grommets of the correct dimensions), cleaned the dial glass and added some heat-shrink tubing to tidy up some frayed cloth covered wire ends on the wires going to the tube caps. I also did a check on alignment on the two wavebands, with only a slight tweak to the upper end of the shortwave band being needed. Four small cork pads on the cabinet feet completed the restoration. Check-out the photos below (click on them for a larger versions) – and yes, that’s the original speaker cloth!

Gerry O’Hara, VE7GUH

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[phil]

Gerry , what a nice radio ! I am happy to hear you got it working and even more important, it looks amazing.
don’t "fret" over the tubes, and if you need others let me know. The dial is something else, I guess you could call this an early crosley "dashboard" 🙂

I found it curious that you used lemon oil with the refinishing, I guess it is a cleaner? I really like Mohawk’s wool soap with fine steel wool for a final rub down ,I like the way it knocks off some of the really high gloss. It sounds like you are learning a lot about refinishing up at SPARC. I am jealous:) Sometimes It’s more about "making" the time to do this stuff than "having" the time I guess.

How would you rate the performance as compared to say, a comparable GE of the time? Rogers had some unique ideas around that time.

Phil

[Gerry O’Hara]

Hi Phil,

Yes, the dial is really nice and the photos don’t really do it (or the cabinet) justice. The dial is backed with a ‘suadette’ finish that is in really good condition considering the state of the chassis and cabinet ‘as found’. This gives a rich-looking contrast to the scale lettering.

This model has an RF stage and a triple-tuned first IF transformer that gives it the edge on sensitivity and selectivity over many contemporary sets I am certain – not sure how it compares with a similar GE table-top though.

The lemon oil is dual-purpose: it lubricates the sandpaper and conditions the dried-out wood surface beneath the old lacquer. Given a couple of days after application the surface takes lacquer without a problem. I have bought some soap-oil (‘Murphy’s’) that is reported to be good for cleaning soiled wood but have not tried it yet.

Gerry

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